Synthesis and characterization of non-stoichiometric LaFeO3 perovskite

La(1-epsilon)FeO(3 - 1.5 epsilon) perovskite catalysts (epsilon = 0, 0.1, 0.2, 0.3) are synthetized by low-temperature thermal decomposition of La and Fe nitrates and further heating to 873 K in air. They are characterized by DTA, XRD, BET, SEM, Mossbauer spectroscopy and tested for the catalytic combustion of methane. All oxides are monophasic; for epsilon = 0 the structure is orthorhombic, whereas for 0 < <epsilon> less than or equal to 0.3 a pseudocubic symmetry is evident. The Mossbauer spectra are characterized by antiferromagnetic sextuplets: for a = 0:3 a doublet is also present. The catalytic activity toward CH, oxidation appears to be strongly enhanced in the samples a with epsilon > 0; the most active composition corresponds to epsilon = 0.1, while for epsilon = 0.2 and 0.3 the catalytic activity is slightly decreased. The results are explained assuming that the excess of iron oxide in the epsilon > 0 samples corresponds to the presence of surface of layers of FeO5 polyhedra, coordinatively unsaturated, according to proposed structural model. (C) 2001 Elsevier Science B.V. All rights reserved.